Some guides to REW and acoustic measurement

[John Mulcahy]

During the check level test, I am not able to have the input meter read -18 dbFS without getting feedback

You have to set up the interface so there is no monitoring, the input must not be mixed back into the output. The only signal going to the output should be from REW.

 

[livnluv]

You have to set up the interface so there is no monitoring, the input must not be mixed back into the output. The only signal going to the output should be from REW.

Good morning Mr. Mulcahy,

Roger. Thanks!

 

[Desmond74]

Is that possible to generate average spectrogram from multiple measurements?

 

[AustinJerry]

Is that possible to generate average spectrogram from multiple measurements?

Well, you can generate an average of several measurements, and then show the Spectrogram of the averaged measurement. Not sure why you would want to do this. What do you think the spectrogram of several averaged measurements tell you?

 

[Desmond74]

Well, you can generate an average of several measurements, and then show the Spectrogram of the averaged measurement. Not sure why you would want to do this. What do you think the spectrogram of several averaged measurements tell you?

I can generate an average of several measurements, but can't generate spectrogram from that average of several measurements. The "Generate" button is grey out.

 

[AustinJerry]

I can generate an average of several measurements, but can't generate spectrogram from that average of several measurements. The "Generate" button is grey out.

Well, I have to admit that I have never tried it. You didn't answer my question. What value would an averaged Spectrogram have? A Spectrogram shows bass resonances, which are standing waves. What would an average of stamding waves represent?

 

[John Mulcahy]

Is that possible to generate average spectrogram from multiple measurements?

You would need to make a vector average so that the result had an impulse response. If the measurements are made from different positions they should be time aligned or cross-correlation aligned first. Cross correlation alignment is a feature of the V5.20.14 early access builds.

 

[Desmond74]

Thanks John. I also found out that by generating minimum phase with the average trace, it will also have an impulse response, and being able to generate spectrogram.
How is that different to a vector average? And why is that multiple measurements from different position should be time align?

 

[John Mulcahy]

The minimum phase is, as it says, producing an impulse response which has the same magnitude response but whose phase is generated from the magnitude response using an assumption of minimum phase. Actual in-room responses are rarely minimum phase across their frequency span, so the spectrogram does not reflect the system that was measured. A vector average uses the measured data, but if the measurements are not time aligned there will be phase cancellations in the average due to their differing time delays.

 

[Desmond74]

Thank you John!!!

 

[giordy60]

hi John
what is the latest release of REW usable on mac os big sur ?
thank you

 

[John Mulcahy]

The current release is on the REW site, the current development build at the moment is the 5.20.14 early access version.

 

[giordy60]

ok thanks, it's the release I already installed !
I thought there was one more recent